Is there a iphone app (3rd party) that will let me set the date and the time for an alarm to sound?

My "Reminders" app doesn't work and Apple support has tried everything. So they now think perhaps something might be wrong with my iCloud and want me to erase my iPhone, so they can access iCloud & check it.
BUT if something's wrong with iCloud, how can I be sure I'll be able to restore all my iPh content??